1. Field of the Invention
The present invention is directed to a method for surface treatment of a semiconductor substrate. More particularly, the present invention is directed to a stripping and cleaning agent for removing dry-etching photoresist residues, and a method for forming an aluminum based line pattern characterized in that a side wall protection film formed in a dry-etching step is removed from the semiconductor substrate.
2. Description of the Related Art
Recently, in an aluminum wiring technique in which a logic LSI or memory KSI is formed on a semiconductor wafer comprising a silicon single crystal, electro-migration and stress migration, etc., occur with increased density of the integrated circuit. These migrations are inhibited by using an aluminum alloy (Al--Si--Cu etc.) as a wire material containing a small amount of Cu, etc.
The process for making a wiring body from an aluminum alloy is as follows:
First, (1) a film or layer of the above-described Al--Si--Cu alloy is sputtered onto a semiconductor wafer having thereon a diffusing layer and an electrical insulating layer.
Next, (2) a resist film or layer is applied onto the Al--Si--Cu layer. Then, a fine pattern is formed thereon using a photolithographic technique.
Then, (3) the resist film is cured by irradiating the entire area of the semiconductor substrate with UV light, to thereby increase the dry-etching resistance of the resist pattern.
Furthermore, the above-described Al--Si--Cu alloy layer is dry-etched using the resist pattern as a mask to form a line pattern.
In this process, a chlorine containing gas, such as BCl.sub.3 --Cl.sub.2, etc., or a gas further containing a Freon series gas, such as CF.sub.4 and CHF.sub.3 etc., is usually used as a dry-etching gas. A side wall protection film which is a reaction product of the etching step becomes attached on the side wall of the pattern of the resist film and the Al--Si--Cu alloy layer. On the other hand, the chlorine gas used in the dry etching step reacts with aluminum in the wiring body to form a compound, such as aluminum chloride, in the side wall protection film. The aluminum chloride reacts with water in the air to form hydrogen chloride. The hydrogen chloride corrodes the Al--Si--Cu alloy and this causes the wire to snap. This type of corrosion is described in Monthly SEMICON NEWS, October 1988, at page 44. To prevent such corrosion, methods comprising heating the wafer after the etching step, or using purified water for cleaning, etc., have been proposed. However, good results are not obtained from these methods. Namely, to prevent the above-described corrosion, the side wall protection film should be completely removed.
Methods that have been proposed for removing the side wall protection film usually include the use of a wet stripping and cleaning agent, such as an organic stripping and cleaning agent, an acidic stripping and cleaning agent and an alkaline stripping and cleaning agent. However, it is difficult to completely release the side wall protection film by using these stripping and cleaning agents. Furthermore, in the case of an organic stripping and cleaning agent, high temperature heating is necessary and an organic solvent, such as isopropanol, etc., is necessary as a rinse liquid. Thus, this technique is complicated and also presents a safety problem.
In the case of an acidic and an alkaline stripping and cleaning agent, the aluminum alloy layer tends to corrode. Thus, these stripping and cleaning agents cannot be used to process an extremely fine line pattern.
Therefore, there is a need in the art for a stripping and cleaning agent and a method for forming a line pattern using such a liquid to completely release the side wall protection film, which stripping and cleaning agent does not corrode a wiring body comprising aluminum.